Device and method for the optical measurement of an optical system by using an immersion fluid

ABSTRACT

A device for the optical measurement of an optical system, in particular an optical imaging system, is provided. The device includes at least one test optics component arranged on an object side or an image side of the optical system. An immersion fluid is adjacent to at least one of the test optics components. A container for use in this device, a microlithography projection exposure machine equipped with this device, and a method which can be carried out with the aid of this device are also provided. The device and method provide for optical measurement of microlithography projection objectives with high numerical apertures by using wavefront detection with shearing or point diffraction interferometry, or a Moiré measuring technique.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toU.S. application Ser. No. 11/080,525, filed on Mar. 16, 2005, which is acontinuation-in-part of International Application PCT/EP2003/014663,with an international filing date of Dec. 19, 2003, which was publishedunder PCT Article 21(2) in English, and the disclosure of which isincorporated into this application by reference; the followingdisclosure is additionally based on German Patent Application No. 102 61775.9 filed on Dec. 20, 2002, which is also incorporated into thisapplication by reference.

BACKGROUND

1. Field of the Invention

The invention relates to a device and a method for the opticalmeasurement of an optical system, in particular an optical imagingsystem, having one or more object-side test optics components to bearranged in front of the optical system to be measured, and/or one ormore image-side test optics components to be arranged behind the opticalsystem to be measured, to a container which can be used for such adevice, and to a microlithography projection exposure machine equippedwith such a device. The designations “object-side” and “image-side”indicate, in the way they are used specifically in the case of opticalimaging systems, that the relevant test optics component is intended forpositioning in the beam path of a used measuring radiation in front or,respectively, behind the optical system to be measured.

2. Description of the Related Art

Such devices and methods are known in various forms, in particular formeasuring optical imaging systems with regard to aberrations. One fieldof application is the highly accurate determination of aberrations ofhigh-aperture imaging systems such as are used, for example, inmicrolithography systems for patterning semiconductor components bymeans of the so-called wavefront detection using shearinginterferometry, point diffraction interferometry and other known typesof interferometer such as the Ronchi type and Twyman-Green type, or bymeans of Moiré measuring techniques. In most cases of these techniques,a periodic or wavefront-forming structure is arranged on the object sideand imaged by the optical imaging system to be measured, and broughtinto superimposition or interference with the periodic structureprovided on the image side. The interference or superimposition patternproduced can be recorded with the aid of a suitable detector andevaluated in order to adjust and/or qualify the optical imaging system.When the same radiation, for example UV radiation, is used for wavefrontmeasurement as is used by the optical imaging system in its normaloperation, it being possible for the measuring device to be integratedin one component with the imaging system, this is also denoted as aso-called system or operational interferometer (OI). A device of thistype is disclosed, for example, in laid-open publication DE 101 09 929A1.

Various methods are known in the literature for increasing theresolution of an optical imaging system, such as reducing the wavelengthof the light used in the imaging, and increasing the image-sidenumerical aperture of the imaging system. The latter is achieved inso-called immersion objectives by using an immersion fluid: see, forexample, the projection exposure machines operating with immersion asdisclosed in laid-open publications JP 10303114 A and JP 12058436 A.

On the basis of shearing interfermetry, such an OI device usuallycomprises an illuminating mask, also termed coherence mask, and anupstream illuminating optics on the object side, that is to say on theobject side of the optical system to be measured, also denoted below asOUT (object under test). Adjoining the OUT on the image side is adiffraction grating, followed by a detector element such as a CCD array,with the optional interposition of imaging optics which project the exitpupil of the OUT onto the detector plane of the detector element. It ismostly the case that the coherence mask is arranged in the object plane,and the diffraction grating is arranged in the image plane of the OUT.In accordance with the spacing conditions to be observed for the opticalbeam guidance, there are respective interspaces between the object-sidelast test optics component of the measuring device and the OUT, betweenthe OUT and the image-side first test optics component of the measuringdevice, and/or between respectively consecutive test optics componentson the object side and/or the image side of the OUT.

These interspaces are customarily either open, that is to say in theinterspaces the radiation used traverses an atmosphere which correspondsto that of the system neighbourhood, for example air, nitrogen or avacuum atmosphere, or closed, and are operated or purged with the aid ofa prescribed gas atmosphere.

Under these conditions, it is normally possible to use such measuringdevices to measure imaging systems up to numerical apertures of theorder of magnitude of 0.95. The measurement of objectives of highernumerical aperture of the order of magnitude of 1.0 and above, as in thecase of objectives which are used in immersion and near-fieldlithography, is therefore scarcely possible.

A primary technical problem underlying the invention is to provide adevice of the type mentioned at the beginning which, with relatively lowoutlay, permits even optical imaging systems of very high numericalaperture to be measured, and can be of relatively compact design, toprovide a corresponding method and a container suitable for use in sucha device, and to provide a microlithography projection exposure machineequipped with such a device.

SUMMARY

The invention solves this problem by providing, in various aspects andformulations, a device, a container, a microlithography projectionexposure machine, and a method having the features set forth in theindependent claims and the description below.

In the device according to the invention, an immersion fluid can be and,in operation, is introduced adjacent to at least one of the one or moreobject-side test optics components and/or image-side test opticscomponents. By contrast with a beam guidance without an immersion fluid,the beam guidance thereby enabled with the aid of immersion fluidpermits the beam aperture angle or beam cross section to be reducedwithout loss of information in conjunction with an otherwise identicalsystem dimensioning. Consequently, it is possible in this way to measurewith sufficient accuracy even optical imaging systems with a very highaperture of the order of magnitude of 1.0 and more, for example usingshearing interferometry wavefront detection. Furthermore, this resultsin the possibility of a very compact design of the measuring device.

In a development of the invention, one or more interspaces are formedbetween respectively two consecutive object-side test optics components,between respectively two consecutive image-side test optics components,between an object-side last test optics component and the followingoptical system to be measured, and/or between the optical system and afollowing, first image-side test optics component, and at least one ofthe interspaces forms an immersion fluid chamber for introducingimmersion fluid. It is possible in this way for an immersion fluid to beintroduced into a chamber at any desired point between two test opticscomponents of the measuring device and/or between the optical system tobe measured and a neighbouring test optics component.

A development of the invention is directed specifically at aninterferometry measuring device which has on the image side in acustomary way an interference pattern generating structure and adetector element. At least one immersion fluid chamber is formed betweenthe test component and image-side interference pattern generatingstructure, and/or between the latter and a following test opticscomponent and/or between the detector element and a preceding testoptics component. The use of an immersion fluid between the image-sideinterference pattern generating structure and detector element permits areduction in the beam aperture angle between these two test opticscomponents, and a more compact design of the arrangement. In addition,advantages result with regard to the signal-to-noise ratio.

A development of the invention provides an interferometry device forwavefront detection which includes on the object side an interferencepattern generating structure and upstream illuminating optics, at leastone immersion fluid chamber being formed between the illuminating opticsand the object-side interference pattern generating structure and/orbetween the latter and the test component. This also contributes to thefact that test components with a high aperture of, for example, 1.0 ormore, such as projection objectives of microlithography systems, can bemeasured with the aid of this device without any problem.

In a development of the invention, the device is designed formeasurement by means of shearing or point diffraction interferometry.

In a development of the invention, the device is of the dual-passreflective type as an alternative to a single-pass design, which is alsopossible. Whereas in the case of the latter the radiation passes throughthe OUT only once, in the case of the dual-pass type it is directed backthrough the OUT by an image-side reflector element, and the detection isperformed on the object side, that is to say on the same side of the OUTon which the other object-side test optics components, such as anobject-side interference pattern generating structure and/orilluminating optics, are located. Such a dual-pass device can be, forexample, of the type of a Twyman-Green interferometer.

In a development of the invention, the device comprises a device forcontinuous or intermittent exchange of immersion fluid, for example in arespective immersion fluid chamber.

In a refinement of the invention, a bellows arrangement, a sealing brushand/or sealing bar arrangement and/or a labyrinth seal arrangementare/is provided as transverse bounding of the respective immersion fluidchamber, which is bounded axially by the two adjacent opticalcomponents. Such seals are comparatively easy to implement and can alsobe used, in particular, in OI arrangements of microlithographyprojection objectives.

In one advantageous development of the invention, a quantum converterlayer and/or at least one lens element and/or at least one liquiddroplet are/is arranged on a radiation exit surface of a structuresubstrate as an image-side test optics component, which, for example,has an interference pattern generating structure. This measure makes itpossible to avoid total internal reflection on this radiation exitsurface of the structure mount, even for high beam angles, such as thosewhich can occur, for example, in the case of large-aperture objectivesto be measured, such as immersion objectives.

In one development of the invention, a fixed arrangement comprising astructure mount and downstream optics, such as a microscope objective orimaging optics, is provided as two image-side test optics components.This makes it easier to adjust these test optics components and,furthermore, contributes to keeping an area in which the opticalcharacteristics are corrected small, thus simplifying the design andproduction of the microscope objective. If required, this measure can becombined with the fitting (as mentioned above) of one or more lenselements, one or more liquid droplets and/or a quantum converter layeron the radiation exit surface of the structure mount.

In a further refinement, an immersion liquid can be introduced into aspace between the optical system to be measured and the structure mount,adjacent to a radiation inlet surface of the structure mount,advantageously combined with the measures mentioned above forarrangement of a quantum converter layer and/or at least one lenselement and/or liquid droplet on the radiation exit surface of thestructure mount, and/or the fixing of the structure mount and microscopeobjective relative to one another.

In a further refinement of the invention, an immersion liquid can beintroduced into a space between the structure mount and a downstreamdetector element, for example a CCD array, adjacent to the radiationexit surface of the structure mount. In this case, the detector elementor some other test optics component which is adjacent to the immersionliquid may be provided with a protection layer, thus protecting itagainst the influence of the immersion liquid.

The measures mentioned above for avoidance of total internal reflectionadvantageously allow multichannel wavefront measurement when required,even for very large aperture objectives, that is to say a parallel,simultaneous measurement on a plurality of measurement channels, that isto say field points, for example by lateral shearing interferometry.

In a development of the invention, a periodic structure used for formingan interference pattern or superimposition pattern is located in acontainer which is filled for the purpose of measuring with immersionfluid which covers the periodic structure. The container is positionedbehind the optical system to be measured in such a way that an exit-endoptical element of the optical system makes contact with the immersionfluid. For example, the interspace between the exit-end optical elementof the optical system and the periodic structure can be completelyfilled with the immersion fluid. The container can, for example, bepositioned such that the periodic structure lies in the image plane ofan imaging system to be measured, or near the same.

In accordance with the invention, a container suitable for use in adevice for measuring an optical system has a window inserted in afluid-tight fashion into a cutout in the container wall. The window canbe designed as an associated test optics component with the periodicstructure, or the relevant test optics component is positioned in frontof the window in the container. With the aid of the window, theinterference pattern or superimposition pattern, which is formed, forexample, approximately in the plane of the periodic structure, can beobserved through the container wall such that an associated detectorneed not be arranged inside the container, and thus inside the immersionfluid, but can be positioned externally. Alternatively, or in additionto the abovementioned use on the image side, it is also possible toprovide a container with an associated object-side test optics componentfor the purpose of object-side positioning.

In a refinement of the container, the window is made from fluorescingmaterial. This permits a visualization of the radiation or theinterference pattern or superimposition pattern even in cases in whichoperation is performed with invisible radiation, for example with UVradiation. In the case of the use of the Moiré measuring technique, thismeasure can render it possible for the detector to access the apertureof the Moiré strips more easily.

In an advantageous development of the invention, the said device has acontainer of the type according to the invention.

A device developed further in accordance with the invention serves formeasuring optical systems by means of Moiré measurement technology. Forthis purpose, there is arranged in front of the optical system aperiodic structure which generates a Moiré superimposition pattern withthe image-side periodic structure. Normally, for this purpose theperiodic structure on the image side, that is to say behind the opticalsystem, is identical to or at least very similar to that on the objectside, that is to say in front of the optical system, and the scale ratioof the two structures corresponds to that of the magnification ratio ofthe optical imaging system under test. The evaluation of the generatedMoiré superimposition pattern can provide information on distortions andfurther aberrations of the optical system.

In an advantageous design of the device, the container is open at thetop, and the opening is dimensioned such that when the container ispositioned below the exit-end optical element of the optical system, agap remains between this element and the container wall. For the purposeof adjustment and/or measurement, the container, and thus the periodicstructure, can be moved by this gap using a suitable positioning devicein any desired spatial directions relative to the exit-end element ofthe optical system. The gap also permits direct access to the immersionfluid, for example in order to eliminate disturbances to the beam pathas a consequence of striations, gas bubbles or heat.

The measuring device according to the invention is integrated in themicrolithography projection exposure machine according to the invention.In this case, the exposure machine can be, in particular, one of thecustomary types of scanner or stepper. The integrated measuring devicecan be used to measure a projection objective of the exposure machine insitu, that is to say there is no need for dismantling.

The method according to the invention can be carried out, in particular,with the aid of the device according to the invention.

DESCRIPTION OF DRAWINGS

Advantageous embodiments of the invention are illustrated in thedrawings and described below. In the drawings:

FIG. 1 shows a diagrammatic side view of an OI device for measuring anobjective, for example used in a microlithography projection exposuremachine, by means of shearing interferometry wavefront detection withthe aid of immersion fluid and sealing bellows,

FIG. 2 shows a diagrammatic side view of the image-side part of an OIdevice similar to FIG. 1, but for a variant without additional imagingoptics between a diffraction grating and a detector element,

FIG. 3 shows a diagrammatic side view of the image-side part of an OIdevice similar to FIG. 2, but for a variant with labyrinth seal andsealing brush or sealing bar arrangements instead of bellows seals,

FIG. 4 shows a diagrammatic side view of the image-side part of an OIdevice similar to FIG. 1 for a variant with a labyrinth seal between theOUT and a diffraction grating, as well as sealing based on surfacetension between the diffraction grating and a micro-objective,

FIG. 5 shows a diagrammatic side view of an OI device according to FIG.1 but in a design for objective measurement by means of pointdiffraction interferometry,

FIG. 6 shows a diagrammatic side view of a device for measuring anobjective, for example used in a microlithography system, by means ofphase-shifting Twyman-Green interferometry,

FIG. 7 shows a diagrammatic side view of a device for measuring anoptical imaging system using Moiré measurement technology,

FIG. 8 shows a schematic side view of the image-side part of an OIdevice analogous to FIG. 1, but for a variant with a quantum converterlayer on a structure mount radiation exit surface,

FIG. 9 shows a schematic side view, corresponding to FIG. 8, for avariant with a lens element on the radiation exit surface of thestructure mount,

FIG. 10 shows a schematic side view, corresponding to FIG. 8, for avariant with additional imaging optics,

FIG. 11 shows a schematic side view, corresponding to FIG. 8, for avariant with immersion liquid between the structure mount and thedownstream detector element,

FIG. 12 shows a schematic side view of the image-side part of an OIdevice, analogous to FIG. 1, for a variant with a structure mount,having a lens element, and a microscope objective, fixed relative to oneanother, and

FIG. 13 shows a schematic side view of an image-side structure mount,corresponding to FIG. 12, but with a liquid droplet arranged on theradiation exit side.

DETAILED DESCRIPTION

The device illustrated in FIG. 1 serves for the optical measurement ofan objective 1, such as a projection objective of a microlithographyprojection exposure machine of the scanner or stepper type forsemiconductor device patterning, the objective 1 being representedmerely diagrammatically by an entrance-end lens 1 a, an objective pupil1 b and an exit-end lens 1 c, which are held in a ring holder 1 d.

On the object-side of the objective 1 to be measured, the measuringdevice includes an illuminating module 2 of which there are shown anilluminating lens 2 a and a following coherence mask 2 b which functionsas an object-side interference pattern generating structure. On theimage side of the objective 1, the measuring device has a diffractiongrating 3, functioning as an image-side interference pattern generatingstructure, a following micro-objective 4 and a detector element 5downstream of the latter. The micro-objective 4 and detector element 5are held in a ring holder 6.

The coherence mask 2 b is in the object plane of the objective 1. Asindicated by a movement arrow B, the diffraction grating 3 is arrangedsuch that it moves laterally in the image plane of the objective 1. Thecoherence mask 2 b and the diffraction grating 3 are provided withsuitable structures for wavefront detection by means of shearinginterferometry, as is known per se.

The micro-objective projects the pupil of the objective 1 onto thedetector element 5, which is implemented as a CCD array of an imagingcamera, for example. The shearing interferometry interference patternspicked up by the detector element 5 are evaluated in an evaluation unit(not shown) for determining the imaging behaviour and/or theaberrations, i.e. imaging errors, or wave aberrations in a conventionalway.

In this respect, the device is of a conventional type and thereforerequires no further explanations. Apart from these conventionalmeasures, it is provided that one or more of the interspaces existingbetween the optical components used are delimited in a fluid-tightfashion by means forming a fluid chamber such that it can be filled withan immersion fluid.

For this purpose, in the example shown in FIG. 1 bellows means areprovided which bound the respective interspace radially, that is to saytransverse to the beam path or the optical axis of the imaging system,while it is bounded axially by the respectively adjacent opticscomponent. In detail, FIG. 1 shows a first bellows 7 a, which bounds theinterspace between the illuminating objective 2 a and the downstreamcoherence mask 2 b with the formation of a first immersion fluid chamber8 a. A second bellows 7 b bounds the interspace between the coherencemask 2 b and the entrance-end lens 1 a of the objective 1 in order toform a second immersion fluid chamber 8 b. A third bellows 7 c boundsthe interspace between the exit-end objective lens 1 c and thedownstream diffraction grating 3 with the formation of a third immersionfluid chamber 8 c. A fourth bellows 7 d bounds the interspace betweenthe diffraction grating 3 and the micro-objective 4 with the formationof a fourth immersion fluid chamber 8 d.

Moreover, the ring holder 6 forms a part of the means forming the fluidchamber, by virtue of the fact that it radially bounds the interspacebetween the micro-objective 4 and detector element 5 in a fluid-tightfashion with the formation of a further immersion fluid chamber 8 e.

Filling the immersion fluid chambers 8 a to 8 e with a respectivelysuitable immersion fluid influences the beam path such that therespective aperture angle and the beam cross section are reduced inconjunction with an otherwise identical system dimensioning, as followsfrom the edge beam path 9 shown diagrammatically in FIG. 1. As aconsequence of this, by comparison with a system design withoutimmersion fluid in the chambers 8 a to 8 e sealed by the bellows 7 a to7 d, it is possible for the objective 1 with a higher numerical apertureto be measured in a spatially resolved fashion over its entire pupil,and/or for the measuring device to be implemented with a more compactdesign.

In alternative embodiments, only one, two, three or four of the fiveimmersion fluid chambers 8 a to 8 e shown in FIG. 1 are formed bydispensing with one or more of the bellows 7 a and 7 d and/or afluid-tight design of the ring holder 6. Instead of the bellows 7 a to 7d or the ring holder 6, it is possible to use any other conventionalmeans forming a fluid chamber in order to seal the relevant interspacebetween two consecutive optics components in each case. As is obvious tothe person skilled in the art, the immersion fluid to be used can beselected in a suitable way, in a fashion adapted to the application,from the fluids known for this purpose, in particular with respect totheir refractive index and with regard to not damaging the adjacentsurfaces of the optics components and the means forming a fluid chamber.Thus, for example, in the case of applications with an operatingwavelength of 193 nm, deionized water with a refractive index of 1.47 issuitable as immersion fluid, it being possible for the respectiveimmersion fluid chamber to have an axial extent of several millimetres.Perfluoropolyether, for example, for which the transmittance isapproximately 90% given an axial length of 50 μm for the immersion fluidchamber, is suitable in the case of an operating wavelength of 157 nm.Further conventional immersion fluids which can presently be used arelithium salts and strontium salts for UV radiation, as well ashalogen-free oil immersions for operating wavelengths below 400 nm, e.g.at 248 nm.

FIG. 2 shows the image-side part of a compact OI variant of FIG. 1,which differs from the exemplary embodiment of FIG. 1 in that thedetector element 5 follows the diffraction grating 3 as the next opticscomponent without the interposition of imaging optics. To easecomprehension, identical reference symbols are chosen in FIG. 2 forfunctionally equivalent component parts, which need not necessarily beidentical. The interspace existing between the diffraction grating 3 andthe detector element 5 is sealed by a bellows 7 e in a fluid-tightfashion radially outwards to form an immersion fluid chamber 8 f.Otherwise, one or more further immersion fluid chambers can be formed inaccordance with FIG. 1 in the upstream system part, for example thethird immersion fluid chamber 8 c, shown explicitly in FIG. 2, betweenthe exit-end objective lens 1 c and the diffraction grating 3.

The introduction of an immersion fluid into the chamber 8 f between thediffraction grating 3 and detector element 5 is particularlyadvantageous in the case of the variant of FIG. 2. This is because, asmay be seen in FIG. 2 with the aid of the edge beam path 9, the apertureangle of the radiation leaving the diffraction grating 3 is reducedcompared to the beam path without immersion fluid, and thus permits theuse of a detector element 5 having reduced areal requirement for thegiven numerical aperture of the OUT. This benefits a more compact designof the overall system.

In the example shown, an immersion fluid with a refractive index greaterthan that of the diffraction grating substrate 3 is selected, with theconsequence that the aperture angle of the radiation is smaller afterexit from the diffraction grating substrate 3 than in the latter.Alternatively, immersion fluids with a lower refractive index than thatof the diffraction grating substrate 3 can be used, as is illustrated inthe example of FIG. 3. If required, it is possible to dispense withotherwise customary antireflection coating on the diffraction grating 3by adapting the refractive indices of immersion fluid and diffractiongrating 3.

A further advantage of introducing an immersion fluid into the immersionfluid chambers formed precisely in the image-side part of the measuringdevice consists in that the signal-to-noise ratio and thus the measuringaccuracy can be improved, since the detected intensity of image pointsin the edge region decreases with the fourth power of the cosine of theaperture angle.

In a view corresponding to FIG. 2, FIG. 3 shows a variant of the compactOI device of FIG. 2 in the case of which the radial sealing of theimmersion fluid chamber 8 c between the exit-end objective lens 1 c andthe diffraction grating 3 is implemented by a bipartite labyrinth seal10 of which an outer cylindrical ring 10 a adjoins the exit-endobjective lens 1 c, and an inner cylindrical ring 10 b is coupled to thediffraction grating 3. The outer ring 10 a is provided on its insidewith a plurality of radially inwardly projecting labyrinth rings whichare arranged at an axial spacing and in whose interspaces radiallyoutwardly projecting labyrinth rings of the inner cylindrical ring 10 bengage such that a narrow labyrinth duct is formed. The narrow labyrinthduct holds immersion fluid in the immersion fluid chamber 8 c because ofits surface tension. At the same time, this labyrinth seal 10 permitsadequate lateral mobility of the diffraction grating 3 with reference tothe exit-end objective lens 1 c by virtue of the fact that the comb-likeinterlocking labyrinth rings can be moved laterally relative to oneanother without varying the width of the labyrinth duct. The lateralmovement of the diffraction grating 3 is effected in this example bymeans of a customary lateral movement actuator 14.

As a further difference from the exemplary embodiment of FIG. 2, in theexample of FIG. 3 the immersion fluid chamber 8 f between thediffraction grating 3 and the detector element 5 is sealed radially by asealing brush arrangement 11 which consists of individual brush hairs 11which project upwards axially from the detector element 5 and arearranged in the shape of a ring. Alternatively, a sealing bararrangement comprising a plurality of coaxial bar rings, which leave anarrow annular gap between them, or a sealing lip arrangement can beprovided. As in the case of the labyrinth seal 10, because of the actionof surface tension or capillary force, the narrow interspaces of thebrushes or bars are sealed by the immersion fluid itself. If required,grooves suitable for amplifying the effect of surface tension can beintroduced into the surface regions relevant to sealing.

In an illustration similar to FIGS. 2 and 3, FIG. 4 shows a furthervariant of the OI device of FIG. 1, which differs from the latter in theimage-end part by virtue of the fact that, firstly, the labyrinth seal10 in accordance with FIG. 3 is provided for sealing between theexit-end objective lens 1 c and diffraction grating 3 and, secondly, useis made for the purpose of sealing the immersion fluid chamber 8 fbetween the diffraction grating 3 and a microscope objective 4 afunctioning as micro-objective solely of the effect of surface tensionor capillary force of the introduced immersion fluid, for which purposean annular groove 12 along the edge region of the plane front side ofthe microscope objective 4 a is provided in a supporting fashion. Thelateral extent of the immersion fluid introduced into the immersionfluid chamber 8 f thus formed stabilizes on the outside by its surfacetension at the annular groove 12 of the microscope objective 4 a withthe formation of a corresponding, outwardly curved edge face 13. It goeswithout saying that this type of sealing is confined to interspaces witha comparatively small axial height. As in the case of theabove-mentioned bellows, brush, bar or sealing lip arrangements, thesealing variant of FIG. 4 also permits an adequate lateral mobility ofthe diffraction grating 3. A lateral relative movement of thediffraction grating 3 relative to the OUT 1 is desired for purposes ofadjustment and for locating the focal position, while a lateral movementof the diffraction grating 3 relative to the detector element 5 ormicro-objective 4, 4 a is desired for the phase-shifting operation ofshearing interferometry.

In the examples shown, it becomes clear that owing to the introductionof immersion fluid between the objective 1 and the image-side grating 3it is possible for the field area defined by the numerical aperture ofthe objective 1 to be imaged completely even in the case of very highaperture values, and that a high resolving power is achieved when themeasuring device is installed as an OI device at the place of use of theobjective 1, for example in a projection exposure machine of amicrolithography system. In normal operation, during the exposureprocess a wafer to be exposed, for example with photoresist, is locatedin the image plane, and so the OI device can advantageously be installedin a stepper or scanner, the immersion fluid chamber corresponding toand even promoting the conditions of use for the latter. Filling one ormore of the object-side interspaces, such as the interspace between theobject-side interference pattern generating structure 2 b, where, forexample, a reticle is located when the objective 1 is in use, and theobjective 1 permits the objective to be designed with smaller lensdiameters.

In addition to introducing immersion fluid in front of themicro-objective 4, 4 a, the latter is designed such that it is suitablefor testing objectives 1 with numerical apertures of up to approximately0.9, since its numerical aperture must be greater than or equal to thatof the OUT 1 if, as desired, the entire objective pupil is to bemeasured. Moreover, it is possible for the very first time in this wayalso to measure objectives with numerical apertures of greater thanapproximately 0.95 or even greater than 1.0 with relatively low outlayby using this technique. If required, an immersion fluid can also belocated in the micro-objective 4, 4 a between optical components of thesame.

In a view corresponding to FIG. 1, FIG. 5 shows an exemplary embodimentof the point diffraction interferometer type. On the object side of theobjective 1 to be measured, this measuring device includes anilluminating module 2′ with an illuminating lens 2 a and a followingpinhole mask 2 c functioning as object-side interference patterngenerating structure. The said mask is arranged in the object plane ofthe OUT 1 for the purpose of generating a first spherical wave. A beamsplitter in the form of a diffraction grating 15 is provided between thepinhole mask 2 c and the entrance-end lens 1 a of the OUT 1, in order togenerate a second spherical wave coherent to the first one.Alternatively, this beam splitter diffraction grating 15 can be arrangedin front of the object-side pinhole mask 2 c or on the image sidebetween the exit-end objective lens 1 c and a further, image-sidepinhole mask 3 a which is preferably located in the image plane of theobjective 1. For the purpose of phase shifting, the beam-splittingdiffraction grating 15 is arranged, in turn, such that it can be movedlaterally by a corresponding lateral movement actuator 16, as symbolizedby the movement arrow B.

The second pinhole mask 3 a, positioned in the image plane or,alternatively, in the vicinity of the image plane of the objective 1,has a second pinhole, in order to generate a spherical reference wave bydiffraction. The radiation for generating the reference wave originatesfrom the imaging by the objective 1 of the first or second of thespherical waves supplied by the beam-splitting diffraction grating 15,which are represented diagrammatically in FIG. 5 by continuous or dashedlines respectively, it being possible for a different diffractionefficiency, and thus different intensities of superimposition to resultdepending on the design of the beam-splitting grating 15. An importantparameter for the intensity of superimposition is also the pinhole size.

Apart from the pinhole, the second, image-side pinhole mask 3 a has, asis usual in the case of point diffraction interferometers, a second,larger opening for the free passage of the OUT wave. The result of thison the detection plane of the detector element 5 is the coherentsuperimposition of reference wave and OUT wave, and the resultinginterference pattern can be detected by the detector element 5 in aspatially resolving fashion, and be evaluated in the usual way by meansof a downstream evaluation unit. The phase shift mentioned isadvantageous here, but not necessary in principle, since the relativetilting of OUT and reference waves results in multiple fringeinter-ferograms from which the phase shift can be calculated with theaid of multiple fringe evaluation methods.

Characteristic, in turn, of the device of FIG. 5 is the formation of theimmersion fluid chambers 8 a, 8 b, 8 c, 8 f from the interspaces betweenthe optics components mentioned with the aid of suitable means formingthe fluid chambers, here, once again by the bellows 7 a, 7 b, 7 c, 7 e,the beam-splitting diffraction grating 15 being arranged inside theimmersion fluid chamber 8 b, or dividing up the latter appropriately. Itgoes without saying that it is also possible to use the abovementioned,alternative means forming fluid chambers instead of the bellows. It alsogoes without saying that in variants of the device of FIG. 5 only someof the interspaces need to be sealed with the formation of a respectiveimmersion fluid chamber.

Whereas the above exemplary embodiments described measuring devices ofthe single-pass type, in the case of which the test radiation is ledonly once through the OUT, FIG. 6 shows a measuring device of thedual-pass type, specifically of the type of a Twyman-Greeninterferometer. Adjoining a light source (not shown), this deviceincludes focusing optics 17 with a pinhole diaphragm as spatial filter,and an adjoining beam splitter 18, of which a first half deflects theradiation by 90° in the direction of the OUT 1, while the remainingradiation is passed without deflection to a reference system part 19with a plane mirror 19 a and an axial movement actuator 19 b with theaid of which the plane mirror 19 a can, as symbolized by double arrows,be moved axially for the purpose of phase shifting.

The radiation fraction reflected by the beam splitter 19 is focused byfollowing focusing optics 20 into the object plane of the OUT 1, inorder to provide a spherical test wave there. A spherical concave mirror21 is arranged on the image side in such a way that its centre ofcurvature lies in the image plane of the OUT 1. Consequently, theradiation emerging on the image side from the OUT 1 is retroreflectedthrough the latter again by the spherical concave mirror 21. In theideal case, that is to say given perfect adjustment and without defectsin the component parts, the outward and returning paths of the wave areidentical. In general, with such dual-pass arrangements the reflectingsurfaces are spherically curved, that is to say formed by concave orconvex glass or mirror members, since the beam path is convergent at theexit end in the case of imaging objectives to be measured. The radiationthen passes via the focusing optics 20 and the beam splitter 19 onto thedetector plane of a detector element 5 a which is arranged behind thebeam splitter 19 and can be an image recording camera, for example. Inaddition, the reference radiation retroreflected by the reference systempart 19 and deflected through 90° by the beam splitter 19 passes to thedetector element 5 a and interferes with the radiation which has passedtwice through the OUT 1, as is usual in the case of the design of theTwyman-Green interferometer.

Characteristically, one immersion fluid chamber 8 b, 8 c is respectivelyformed by means of respective bellows 7 b, 7 c, alternatively, by meansof one or the other, abovementioned sealing variants, on the object sideand image side in a fashion adjacent to the OUT 1, that is to say on theobject side between the focusing optics 20 and the entrance-endobjective lens 1 a, and on the image side between the exit-end objectivelens 1 c and the spherical concave mirror 21. The abovementionedproperties and advantages of filling these interspaces with an immersionfluid are obtained, once again.

The device shown in FIG. 7 likewise serves for the highly accuratemeasurement of optical imaging systems, for example a high-resolutionmicrolithography projection objective, which is illustrated merelydiagrammatically and in an abbreviated fashion with an exit-end element30, such as an exit-end lens, with regard to aberrations, in particulardistortion. For this purpose, the device has an illuminating device 31which can, for example, be a conventional illuminating system of amicrolithography projection exposure machine, specifically in cases inwhich the measuring device is integrated in the exposure machine. Thewavelength of the radiation supplied by the illuminating device 31 canlie, in particular, in the UV or EUV region.

The device also comprises an object-side test optics component 32, whichis preferably to be positioned in the object plane of the projectionobjective and has a periodic structure 32 a which is designed in thisexample as a Moiré pattern, typically with periodic Moiré strips.

The device also includes a container 34 which is to be positioned on theimage side and can be filled with an immersion fluid 35 and has an uppercover 41 on the edge side into which a sufficiently large opening islet, through which the exit-end element 30 of the projection objectivecan pass, a movement gap 39 remaining between the opening edge and thepenetrating optical element 30.

A further periodic structure 36, which is likewise designed as a Moirépattern, is mounted on a window 37 which is inserted in a fluid-tightfashion in a cutout which is provided in a base wall 43 of the container34. Alternatively, the image-side Moiré pattern 36 can also bepositioned above and therefore in front of the window 37 on a carrierelement fitted in the container 34, for example on a carrier plate. Thewindow 37 can optionally be made from a fluorescing material which, inthe event of use of a non-visible radiation such as UV radiation,permits the latter and/or the interference pattern or superimpositionpattern to be visualized.

The device shown can be used to measure the projection objective with alow outlay at its operating site without the need for this purpose toremove it from the microlithography projection exposure machine. Forthis purpose, the object-side Moiré pattern 32 a is brought into itsdesired object-side position, for example by inserting it into the beampath with the aid of a reticle holder in exchange for a reticle in theobject plane which is used in normal operation. The container 34 iscorrespondingly filled with immersion fluid 35 such that the lattercovers the Moiré pattern 36, and is positioned on the image side at asuitable point, for example in the image plane of the projectionobjective. This can be performed, for example, with the aid of a waferholder which is used in normal operation to position a wafer to beexposed in the image plane. In other words, by exchanging the saidcomponents the microlithography projection exposure machine can easilybe switched over from normal operation, that is to say the imaging of areticle positioned in the object plane onto a wafer positioned in theimage plane, to measurement operation. In the measurement operationposition shown, the exit-end element 30 of the projection objective dipsinto the immersion fluid 35, that is to say the latter fills theinterspace between the said objective and the image-side Moiré pattern36.

In the measurement operation shown, the object-side Moiré pattern 32 ais imaged by the projection objective onto the image-side Moiré pattern36, such that superimposition of the image of the object-side Moirépattern 32 a and the image-side Moiré pattern 36 produces a Moirésuperimposition pattern which is observed through the window 37 with theaid of a detector 38. In a way familiar to the person skilled in theart, aberrations, in particular distortion errors, of the projectionobjective are detected by appropriate evaluation of the Moirésuperimposition pattern.

Depending on requirement, the movement gap 39 permits a movement of thecontainer 34 in all spatial directions for the purposes of adjustment ormeasurement, for example a lateral and/or axial displacement, a tiltingand/or rotation such that the container 34, and thus the associatedMoiré pattern 36, can be positioned optimally for the measurementoperation. The movement or positioning of the container 34 isaccomplished by a suitably fitted and designed positioning unit 42. Inaddition, it is optionally possible for the object-side and/orimage-side Moiré pattern 32 a, 36 to be subjected to expansion,contraction or rotation in order to obtain a Moiré strip superimpositionpattern which can be effectively evaluated, and/or to compensateaberrations of the projection objective partially in advance.

The movement gap 39 also permits direct access to the immersion fluid35, and this permits the elimination of disturbing influences exerted bythe latter on the measurement operation, such as striations, gas bubblesor thermal effects.

It goes without saying that the device shown is suitable for measuringnot only a projection objective, but also any other desired opticalimaging systems and other optical systems by means of Moiré measurementtechnology. The invention also comprises devices which are based onother conventional measuring techniques for determining aberrations ofoptical imaging systems and which make use of a periodic structure to bearranged on the object side and/or image side, in order to generate asuperimposition pattern or interference pattern indicating aberrations.The invention is suitable for all normally used radiation wavelengths,such as for the use of an He—Ne laser at 632.8 nm, and other lightsources such as are customary in lithography, in particular includingthose in the UV wavelength region and EUV wavelength region between 10nm and 300 nm.

In all the exemplary embodiments shown, the immersion fluid can beintroduced in a stationary fashion into the relevant immersion fluidchamber or the container, or alternatively, the respective immersionfluid chamber is flushed or refilled continuously or periodically withthe immersion fluid. It is possible in this way to avoid any kind ofdisruptive effect owing to heating of the immersion fluid, and/or toachieve temperature control, for example cooling, of the adjacentoptical components. Suitable conventional means are then provided forthis purpose, in particular an inlet 22 a and an outlet 22 b into orfrom the immersion fluid chamber 8 c, as shown in FIG. 6 by way ofexample for the case of the immersion fluid chamber 8 c. In this way,the immersion fluid 23 can be conveyed in the circulation by means of apump from a storage tank into the corresponding immersion fluid chamber,and extracted therefrom.

FIGS. 8 to 13 show further advantageous embodiments of the image-sidepart of an OI device for measurement of optical systems, in which casethis image-side device part may, of course, also be used, in each casein a suitably modified form, for measurement devices which operate onthe basis of one of the other measurement principles mentioned above.For the sake of clarity, only those components which are essential tothe explanation of the special feature are illustrated, in each caseschematically.

Specifically, FIG. 8 shows an image-side device part with a structuremount 53 which is arranged at a relatively short distance in the beampath behind an objective 51, which is indicated only schematically butis to be measured, and which may, in particular, be a microlithographyprojection objective as in the above exemplary embodiments. An immersionliquid 52, for example water, is introduced into the space between theobjective 51 to be measured and the structure mount 53. On its radiationinlet side facing the objective 51, the structure mount 53 has aconventional interference pattern production structure, which is notshown in any more detail, such as a diffraction grating structure for OImeasurement. A detector element 55, such as a CCD array, is locatedadjacent to the structure mount 53, without any gap, or at a very shortdistance. Alternatively, a faceplate can be inserted between thestructure mount 53 and the detector element, and is mounted on thedetector element 55. A certain distance between the detector element 55and the structure mount 53, with or without a faceplate, reduces thethermal load on the structure mount 53 and the objective 51 caused by adetecting image recording camera.

This compact configuration of the detector part is suitable, forexample, for an OI device which operates on the principle of parallel,that is to say multichannel, lateral shearing interferometry, and whichis able to measure optical systems, in particular with respect to theaberrations which correspond to the Zernike coefficients Z2 to Z37, within-line calibration preferably being provided. This detectorconfiguration is also particularly suitable for measurement of objectswith a very high numerical aperture NA, for example NA>1, as occurs, forexample, in the case of so-called immersion objectives, whose designincludes an immersion liquid.

In a situation such as this, unless further measures are taken, there isa risk of total internal reflection occurring on the radiation exitsurface of the structure mount 53 owing to the high beam angles whichoccur, as is illustrated in FIG. 8 for an incident beam ES by means of areflected beam RS, which is indicated by a dashed line, and is theresult of total internal reflection of the incident beam ES at thisboundary surface of the structure mount 53 with the air. In order toprevent this effect, a quantum converter layer 54 is applied to thisradiation exit surface of the structure mount 53 in the exemplaryembodiment shown in FIG. 8. The material of the quantum converter layer54 is chosen such that it converts the incident radiation to radiationat a different wavelength, at which the total internal reflection effectdoes not occur. For example, the quantum converter layer 54 may bedesigned to transform incident radiation, for example at a wavelength of193 nm to radiation at a sufficiently longer wavelength, for example toradiation at a wavelength of 550 nm.

Quantum converter layers of this type, for examplefluorescent/luminescent layers, are known per se to those skilled in theart and are frequently applied, for example, to a CCD chip for thepurpose of appropriate quantum conversion, so that they do not requireany further explanation here. In the present case, the quantum converterlayer 54 is located on the lower face, that is to say the radiation exitsurface, of the structure mount 53, and the interferogrammes to bedetected are produced in the quantum converter layer 54. The CCD array55 is positioned at a sufficiently short distance, preferably of <10 μm,behind the quantum converter layer 54, in order to minimize striation ofthe radiation emitted from the quantum converter layer 54 into theentire hemisphere and thus of the interferogrammes to be detected on theCCD array 55. Alternatively, the CCD array 55 may be arranged in directtouching contact with the quantum converter layer 54, that is to say thesubstrate mount 53, the quantum converter layer 54 and the CCD chip 55then form a sandwich structure.

FIG. 9 shows a variant of the example shown in FIG. 8, with the samereference symbols being chosen here as in the further FIGS. 9 to 13 aswell, for identical or functionally equivalent elements, for claritypurposes. The exemplary embodiment of FIG. 9 differs from that in FIG. 8in that a lens element 56 rather than a quantum converter layer isfitted to the lower face of the substrate mount 53, that is to say onits radiation exit surface, for example by wringing. The lens element 56may have a hemispherical shape, or, alternatively, an aspherical shape.If required, imaging errors caused by the detection optics formed by thelens element 56 may be corrected in a suitable manner, for example byusing a conventional focus trick technique. Numerical wavefrontcorrection can also be used, for example as described in U.S. patentapplication Ser. No. 10/766,014 from the same applicant, whose contentis hereby included herein, in its entirety, by reference. As issymbolized by the incident beam ES1 which passes through as far as theCCD chip 55 in FIG. 9, the lens element 56 has a beam deflecting effect,which prevents total internal reflection from occurring on the radiationexit surface of the substrate mount 53. In this case, the CCD chip 55 isadjacent to, but at a suitable distance from, the substrate mount 53with the lens elements 56 that has been wrung onto its lower face.

FIG. 10 shows a variant of FIG. 8, in which the interferogramme which isproduced in an active image-producing area 54 b of a quantum converterlayer 54 a on the lower face of the substrate mount 53, does not falldirectly on a CCD chip which is in touching contact or is a shortdistance behind it, but is imaged by means of imaging optics 56 on adetection-active part 55 a of the CCD array, or of the correspondingimage recording camera 55. As in the case of FIG. 8, the quantumconverter layer 54 a to a major extent prevents the occurrence of totalinternal reflection, that is to say the reflected radiation RS marked bya dashed line, for light beams ES which are incident at large angles.

FIG. 11 shows a variant of FIG. 8, in which an immersion liquid 52 a isadditionally introduced into the space between the structure mount 53and the CCD chip 55, as well. This means that there is no boundarysurface between the structure mount 53 and the air, thus avoiding thetotal internal reflection effect caused by this. A quantum converterlayer on the lower face of the structure mount 53 may admittedly beprovided if required, but is not absolutely essential, and FIG. 11 showsthe situation without a quantum converter layer. It is also possible toprovide a quantum converter layer or some other suitable protectionlayer on the CCD chip 55, in order to isolate it and the image recordingcamera from the immersion liquid 52 a, and thus to protect them. Anyother test optics component which is adjacent to an immersion liquid maybe provided with a protection layer such as this in the same way.

It is self-evident that the measures mentioned above relating to theindividual FIGS. 8 to 11 can also be combined in any other desiredmanner. Thus, for example, the lens elements 56 shown in FIG. 9 can beapplied to the quantum converter layer 54 shown in FIG. 8, and/or thespace between the structure mount 53 and the lens element 56 and the CCDchip 55 as shown in FIG. 9 can be filled with the immersion liquid 52 aas shown in FIG. 11, which then surrounds the lens element 56. In afurther embodiment of the invention, which is not illustrated, aplurality of individual lens elements may be fitted to the lower face ofthe structure mount 53 as a variant of FIG. 9.

The measures explained above with reference to FIGS. 8 to 11advantageously provide the precondition to allow even objectives withvery high numerical apertures to be measured on a number of channels bymeans of an appropriate wavefront measurement device, for example adevice which operates with the aid of lateral shearing interferometry,that is to say simultaneously for a plurality of field points.

FIG. 12 shows an exemplary embodiment of the image-side part of ameasuring device, in which a structure mount 53 a in the form of astructure mount 53 shown in FIGS. 8 to 11 and having a lens element 56 afitted to its lower face in the manner of the lens element 56 shown inFIG. 9 is mechanically rigidly coupled to a microscope objective 57 a bymeans of an annular holder 58. As in the example shown in FIG. 9, thelens element 56 a which is wrung onto the lower face of the structuremount 53 a to a major extent avoids the occurrence of total internalreflection even for high incidence angles of the incident measurementradiation ES2, without the need for immersion liquid to be introducedinto the space between the structure mount 53 a with the lens element 56a wrung on it and the microscope object 57 a, although this mayoptionally be provided. For this purpose, the lens element 56 a ischosen such that it decreases the numerical aperture for the radiationES2 to such an extent that all of the required beams can also propagatethrough the air to the microscope objective 57 a and to a downstreamimage recording camera 55 a with a CCD array.

Once again, an immersion liquid 52 a is introduced into the beam pathupstream of the structure mount 53 a, adjacent to its radiation inletsurface, although this is indicated only schematically in FIG. 12. Inthis case, as in the situations in FIGS. 8 to 11, the immersion liquid52 a preferably fills the space between the exit surface of an opticalsystem which is to be measured but is not shown in FIG. 12, in the sameway as a microlithography projection objective, and the structure mount53 a. Only this intermediate space in the detection part of themeasuring device is filled with the immersion liquid 52 a in the exampleshown in FIG. 12, preferably being rinsed although this is notabsolutely essential for the space between the structure mount 53 a andthe microscope objective 57 a, as a result of the arrangement of thelens element 56 a. The microscope objective 57 a images the radiationonto the downstream imaging recording camera 55 a.

Precise lateral and vertical adjustment of the microscope objective 57 arelative to the structure mount 53 a with the associated interferencepattern production structure is of considerable importance for themeasurement process, in particular for an OI measurement. The rigidmechanical coupling of these two components 53 a, 57 a by means of theholder 58 fixes the adjustment parameters, thus avoiding changes tothese parameters. The fixing of the structure mount 53 a and microscopeobjective 57 a relative to one another also makes it possible to keepsmall specific design parameters, such as the area of sine correction,thus simplifying the design, production and manufacture of themicroscope objective 57 a.

As an alternative to the example illustrated in FIG. 12, the lenselement 56 a there may also be omitted, with immersion liquid beingintroduced, instead of this, into the space between the structure mount53 a and the microscope objective 57 a, and/or with a quantum converterlayer being provided on the lower face of the structure mount 53 a. In afurther alternative embodiment, which is not illustrated, the imagingoptics 57 are, as a variant of the exemplary embodiment shown in FIG.10, mechanically rigidly connected to the structure mount 53 via aholder in the form of the holder 58 shown in FIG. 12. A further variantof the example shown in FIG. 12, but which is not illustrated, dispenseswith the rigid mechanical coupling of the structure mount 53 a andmicroscope objective 57 a, and thus with the holder 58.

FIG. 13 shows an alternative to the lens element 56 a on the lower faceof the structure mount 53 a shown in FIG. 12. Specifically, FIG. 13provides for a wetting layer 59 with a wetting subarea 59 a and anon-wetting subarea 59 b, which surrounds the subarea 59 a, to beprovided on the lower face, that is to say the radiation exit surface,of a corresponding structure mount 53 b, and for a hanging liquiddroplet 60 to be attached to the wetting layer area 59 a. This dropletmay, for example, be composed of water, in which case quartz glass, forexample, is then suitable for the wetting layer area 59 a.

The liquid droplet 60 acts as a liquid lens, and with this functionreplaces the wrung-on lens element 56 a in the example in FIG. 12. Theshape of the liquid droplet 60 and thus its optical imagingcharacteristics can be fixed in a desired manner by suitable materialselection for the droplet 60, for the wetting layer area 59 a, and forthe non-wetting layer area 59 b. Liquid lens systems of this type and ofa different type which can be used in the present case and which may,for example, also be composed of a plurality of liquids are known per sefrom the prior art, to which reference can be made, and which thusrequire no further explanation. In operation, the saturation vaporpressure of the liquid which is used for the liquid droplet 60 is set inthe space between the structure mount 53 b and downstream optics by, forexample, preventing any gas exchange between this intermediate space andthe exterior or, when using water for the liquid droplet 60, bymeasuring the moisture content in the intermediate space, and byintroducing water vapor, if required. In alternative embodiments, aplurality of such liquid droplets can also be provided on the lower faceof the structure mount 59 b.

The various embodiments which have been explained above with referenceto FIGS. 12 and 13 for the image-side part of a measuring device aresuitable not only, as mentioned, for OI devices but also, in a possiblysuitably modified form, for measuring devices which are based on othermeasurement principles, for example on point diffraction interferometry.

As the exemplary embodiments shown and described above make plain, theinvention makes available a device with the aid of which it is alsopossible to optically measure very accurately optical imaging systemshaving a very high numerical aperture, for example with the aid of wavefront measurement by means of shearing interferometry or pointdiffraction interferometry. The device can be used, in particular, inthe case of projection objectives in microlithography systems, such asthose of the scanner or stepper type, as an OI arrangement for wavefrontdetection, or as a Moiré measuring arrangement, it being possible tointegrate it into the lithography system itself, if necessary. It goeswithout saying that the measuring device according to the invention canalso be used for the optical measurement of any other optical imagingsystems with the use of interferometric or other conventionalmeasurement techniques, in particular for spatially resolved measurementover the entire pupil area with a high numerical aperture.

By using immersion, for example for the formation of one or moreimmersion fluid chambers in one or more interspaces, traversed by themeasuring optical radiation, between optical components of the measuringdevice and/or between the OUT and respectively adjacent test opticscomponents, it is possible to reduce the aperture angle or the beamcross section of the measuring radiation, and the measuring device canbe of compact design. Although the formation of immersion fluid chambersor the use of a container for the immersion fluid is generallyadvantageous, it is not mandatory. However, the invention also comprisesembodiments in the case of which the immersion fluid is introducedwithout an immersion fluid chamber formed specifically therefor, andwithout a container provided specifically therefor. To be specific, theimmersion fluid may be introduced adjacent to at least one of the one ormore object-side and/or image-side test optics components, so that theguidance of the radiation through the immersion fluid is influenced in adesired way.

The above description of the preferred embodiments has been given by wayof example. From the disclosure given, those skilled in the art will notonly understand the present invention and its attendant advantages, butwill also find apparent various changes and modifications to thestructures and methods disclosed. It is sought, therefore, to cover allchanges and modifications as fall within the spirit and scope of theinvention, as defined by the appended claims, and equivalents thereof.

1. Device for the optical measurement of an optical system, comprisingat least one of: one or more object-side test optics components arrangedin front of the optical system to be measured, and one or moreimage-side test optics components arranged behind the optical system tobe measured, where the device is designed such as to introduce animmersion liquid adjacent to at least one of the one or more object-sidetest optics components and the one or more image-side test opticscomponents.